The present invention relates generally to management of electrically-controlled pneumatic (ECP) trains and, more specifically, to the location and identification of nodes on the train network.
ECP brake systems consist of a network of ECP devices or nodes. The number of devices or nodes on the network varies. A controlling node must be able to locate and retrieve information from every device or node on the network. A general representation of network 10 is shown in FIG. 1 to include the controlling node or device 12 and nodes or devices 14 connected by buss 16 which may be wire or wireless.
The American Association of Railroads (AAR) Intra-Train Communication Specification for Cable-Based Train Control Systems (S-4230) specifies a message for locating network devices. The message contains both a command to enable or disable receiving devices' responses or to query receiving devices to respond and a settable response interval over which receiving devices are to randomize their responses. Section 4.2.1 of the AAR Specification is shown in the Appendix. In the Appendix, HEUs are head end units or locomotives, CCDs are the brake control devices on the cars, PSCs are the power source controllers on the locomotives and EOT is the end of train device.
Typically an “enable response” message is broadcast to all devices on the network by the controlling device. It then broadcasts a query for all devices to respond. All devices which are enabled send a response. For each response, the controlling device normally receives multiple responses per query. It then unicasts a “disable response” command to the responder. The query/receive/disable cycle is repeated until no more responses are received. A flow chart of this process is shown in FIG. 2.
With multiple network devices, there is potential for the network to be overloaded with traffic and for contention problems to arise. The response interval may be used to mitigate this by spreading out responses over a specified interval. The ECP network used has a relatively low bandwidth, and is capable of handling a maximum of approximately 10–12 messages per second. Thus, a system with 500 nodes would require a 50 second response interval. In theory, all of the devices spread their responses over this interval, and the number of nodes attempting to send a response during any given time slice should be constant over the response interval. However, with no prior knowledge of the number of nodes which will respond, choosing an interval is problematic. Too small an interval for the number of responders will cause network contention, while too large an interval will be highly inefficient. This is compounded by the necessity of repeating the query phase until no responses are received to ensure all devices have been located.
A method of identifying power source nodes in the network is described in U.S. Pat. No. 6,225,919. Following the identification process, serialization (or the order of the nodes in the train) is determined using one of the methods of U.S. Pat. Nos. 5,966,084 and 6,160,619.
The present invention is a method of locating nodes in train having at least one node per car and includes enabling each node; querying each enabled node to respond during a response interval; disabling each node which responded; and re-querying the enabled nodes until no further responses are received during a response interval. The method further includes determining the number of responses during a present response interval and setting the length of a subsequent response interval as a function of the determined number of responses. The number of responses may be determined for a whole interval or for a portion of the present response interval, and the length of the subsequent response interval is set based on the response rate determined for the whole or portion of the present response interval. The subsequent response interval may be initiated before the expiration of the present response interval if a new interval length is to be set.
The method may further include determining if a response has not been received before expiration of a wait period between responses and performing the determining of the number of responses and setting the interval length if the wait period has expired. The setting of the interval length may be performed after expiration of either one or both of the wait period and the response interval. The disabling may be performed after the expiration of one or both of the wait period and the response interval or before the expiration of the response interval.
An initial response interval length may be set based on the anticipated number of active nodes and anticipated response rate. The number of active nodes that have not responded may be estimated, and the length of the subsequent interval is set as a function of the number of active nodes that have not responded. The rate of response is determined, and the length of the subsequent interval is set as a function of both the number of active nodes that have not responded and the determined response rate.
The method may also be enabling each node; querying each enabled node to respond during a response interval; disabling each node which responded after expiration of the response interval; and re-querying the enabled nodes during subsequent response intervals until no further responses are received during a response interval. Alternatively the method may be enabling each node; querying each enabled node to respond during a response interval; determining if a response has not been received before expiration of a wait period between responses; disabling each node which responded before expiration of the response interval if it has been determined that a response has not been received before the wait period has expired; and re-querying the enabled nodes during subsequent response intervals until no further responses are received during a response interval. Either of these methods may be used alone or with the method of changing the length of the response interval.
Other advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.